Plate and Frame Filter Presses

Plate and Frame Filter Presses mechanically dewater sludge by forcing water through filter media under hydraulic pressure, typically achieving 18-25% dry solids content from feed sludge containing 2-4% solids. The system alternates between rigid plates and flexible frames lined with filter cloth, creating chambers that fill with sludge under 100-225 psi pressure. Water passes through the cloth while solids form filter cake. Municipal plants from 0.5-50 MGD commonly use these units for biosolids dewatering, processing 50-500 GPM of sludge. The primary limitation is batch operation requiring 2-4 hour cycles, making continuous operation impossible without multiple parallel units.

• Biosolids Dewatering (Primary Application): Plate and frame presses handle 2-15% solids feed from gravity thickeners or DAF units, producing 18-25% solids cake. Selected for superior cake dryness compared to belt presses, reducing disposal costs by 20-30%. Upstream: polymer feed systems and feed pumps. Downstream: cake conveyors to storage bins.
• Water Treatment Residuals: Dewater alum/iron sludge from clarifiers and filter backwash holding tanks. Handles 0.5-3% solids feed, achieving 15-20% cake solids. Chosen for intermittent operation matching WTP production cycles. Critical for plants without lagoon space.
• Lime Softening Sludge: Process calcium carbonate sludge from softening plants. Feed typically 3-8% solids, producing 25-35% cake due to excellent drainage characteristics. Selected where cake quality justifies higher capital cost versus continuous systems.

Daily Operations: Monitor feed pressure (typically 50-150 PSI), filtrate clarity, and cycle times (2-6 hours total). Adjust polymer dosing based on cake release and filtrate quality. Track plate closing pressure and hydraulic system performance. Modern systems provide automated sequencing with minimal operator intervention during normal cycles.

​

Maintenance: Weekly cloth inspection and high-pressure washing (2000-3000 PSI). Monthly hydraulic fluid checks and plate alignment verification. Annual cloth replacement and hydraulic seal service. Requires confined space training for plate chamber access. Standard PPE plus respiratory protection during cake discharge operations.

​

Troubleshooting: Cloth blinding causes extended cycle times and poor cake formation - indicates inadequate pretreatment or polymer dosing. Hydraulic leaks create uneven closing pressure and cloth damage. Plate warping from thermal cycling reduces sealing effectiveness. Typical cloth life 12-36 months, plates 15-20 years with proper maintenance.

• Filter Plates: Cast iron or polypropylene construction, 630-1500mm square typical for municipal use. Recessed or membrane plates create 25-40mm thick chambers. Selection based on pressure rating (6-15 bar), chemical compatibility, and required cake thickness.
• Hydraulic Closing System: Provides 2000-8000 kN closing force via hydraulic cylinder and pressure multiplier. Maintains consistent sealing pressure throughout cycle. Sizing based on plate area and operating pressure.
• Cloth Filter Media: Polypropylene or polyester fabrics, 1-100 micron retention. Monofilament weaves for easy release, multifilament for fine particle retention. Service life 1-3 years depending on feed characteristics and washing frequency.
• Feed Pump System: Progressive cavity or diaphragm pumps delivering 50-500 GPM at 50-220 PSI. Must handle 2-15% solids without shearing floc. Sized for 1-4 hour fill cycles based on chamber volume.

• Solids Loading Rate: 2-8 lb/ft²/hr for typical municipal sludge applications, with 4-6 lb/ft²/hr being optimal for consistent cake formation and reasonable cycle times.
• Operating Pressure: 100-225 psi maximum working pressure, with most municipal applications operating at 150-180 psi. Higher pressures (200+ psi) used for difficult-to-dewater biosolids.
• Filter Area: Individual plate sizes range from 630mm to 2000mm square, with 1000-1500mm plates most common for municipal plants. Total filter area typically sized at 0.5-2.0 ft² per GPM of sludge flow.
• Cycle Time: 2-6 hours total cycle time, including 1-3 hours filling, 0.5-2 hours pressing, and 15-30 minutes discharge. Longer cycles (4-6 hours) typical for lime-conditioned sludge.
• Cake Thickness: 15-40mm typical cake thickness, with 20-25mm optimal for most municipal applications. Thicker cakes require longer cycle times but reduce handling frequency.
• Solids Concentration: Feed solids of 3-8% typical, producing cake solids of 35-45% for biological sludge, 45-55% for chemical sludge. Polymer dosing at 8-15 lb/dry ton solids.
• Filtrate Quality: <50 mg/L TSS typical, <100 mg/L TSS maximum for return to plant headworks.

• What feed solids concentration and polymer conditioning strategy will optimize cycle economics? Feed solids below 3% result in excessive cycle times and poor economics, while above 8% causes premature cloth blinding. Polymer overdosing (>20 lb/dry ton) increases chemical costs without proportional dewatering improvement. Poor conditioning decisions increase operating costs by 40-60%.
• How many chambers are needed to match plant hydraulics and provide operational flexibility? Chamber count affects capital cost, footprint, and operational complexity. Undersizing by >20% creates bottlenecks during peak flows. Oversizing wastes capital and increases maintenance. Need detailed mass balance with peak month solids production and desired operating schedule (5-day vs 7-day operation).
• What cloth material and weave pattern will provide optimal service life for specific sludge characteristics? Polypropylene cloth for standard municipal sludge, PTFE for aggressive chemical conditioning. Fine weave (4-7 CFM) for biological sludge, medium weave (10-15 CFM) for chemical sludge. Wrong cloth selection reduces service life from 18-24 months to 6-12 months, doubling replacement costs.
• Should automatic or manual plate shifting be specified based on labor availability and throughput requirements? Manual systems reduce capital cost by $100,000-200,000 but require 2-3 operators per cycle. Automatic systems justified for plants >5 MGD or where labor costs exceed $30/hour loaded rate.

• Primary: Division 46 23 61 - Sludge Dewatering

• Material/Equipment Verification: Verify 316SS construction for all wetted parts, Confirm plate gasket materials (EPDM standard), Check hydraulic system specifications and backup power requirements
• Installation Requirements: Requires 10-15 ft overhead clearance for plate maintenance, Foundation must handle 150-200% of operating weight when loaded, Dedicated wash water supply (40-60 gpm at 80 psi minimum)
• Field Challenges: Filtrate piping prone to plugging during startup, Cake discharge conveyor alignment critical
• Coordination Issues: Polymer feed system integration requires early coordination, 16-20 week lead times typical

• Alfa Laval - AutoMatos series (municipal biosolids focus)
• Andritz - KMPT series with automated cake discharge
• JWI/Filter Specialists Inc. - VariDry models (popular in smaller municipalities)
• Komline-Sanderson - KomPress series with polymer conditioning integration

​

All maintain strong municipal references, with Alfa Laval and Andritz dominating larger installations (>5 MGD), while JWI serves the 0.5-5 MGD market effectively.

• Belt Filter Presses - Lower capital cost, higher labor requirements, 15-20% cake solids typical. Preferred for smaller plants (<2 MGD) with limited operator staffing.
• Centrifuges - Higher throughput, automated operation, but 25-30% higher power costs and more complex maintenance. Better for larger facilities (>10 MGD) with skilled maintenance staff.
• Screw Presses - Emerging technology, lower polymer usage, but limited municipal track record. Cost comparable to belt presses.

Establish strong manufacturer service relationships early - filter press troubleshooting requires specialized expertise that most plant staff lack initially. Negotiate comprehensive training packages including hands-on operation and maintenance. Consider purchasing spare plate gaskets and filter cloths during initial procurement to avoid 4-6 week lead times. Many plants save 15-20% on lifecycle costs by standardizing on single manufacturer across multiple units for parts commonality.